This invention relates generally to electrical circuit breaker devices and more specifically to a double break trip-free circuit breaker which is ambient temperature compensated.
Various electrical and electro-mechanical circuits in the event of an electrical, mechanical or human failure can receive current surges which are potentially destructive to the individual electrical components. Therefore, circuit breakers are normally employed in such circuits so that if a high current condition occurs - because of a short or a current surge - the circuit will be interrupted. Normally, these circuit breakers are placed in the current path to various components which require their protection such that a high current load will cause the circuit breaker to interrupt the current flow to the device. In addition to their basic protection requirement, it is also advantageous for them to be small, light-weight, easily manufactured, etc. Examples of this type of circuit breaker are in U.S. Pat. Nos. 3,007,018 and 3,617,971.
There are a number of features which are particularly desirable in a circuit breaker which hitherto have not existed in any combination. A problem that has existed with past circuit breakers is the extreme amount of wear in the contacts, the point at which the electrical circuit is made and broken. These normally wear a little bit every time a circuit is made and every time it is broken there is a small amount of arcing resulting in the deposition of metal across the contacts. Over a period of time this makes the contacts unsuitable for making and breaking circuits. Either the circuit is not completely shorted or else it is never completely opened necessitating replacement of the entire circuit breaker. Additionally, circuit breakers of the single break type, that is having only one set of contacts, require a much larger contact area to have the same wear characteristics as the double break type contacts.
A double break contact circuit breaker has two sets of making and breaking points which operate simultaneously to provide two arc points and allow interruption of a higher current load than the single break contact having the same contact area. A problem in the double break contact type circuit breaker is the fact that during manufacture it is often difficult to perfectly align the two sets of breaker points and, of course, if both breaker points do not make and break at the same time the advantages of the double break circuit breaker are lost, and there is a possibility of the circuit breaker not making a complete circuit even when properly reset.
Many of the small, low capacity circuit breakers have a heater element and a bimetallic strip to provide the current sensing feature. However, the heat required to bend the bimetallic strip away from its latched position can vary considerably with variations in the ambient temperature. Therefore the temperature of the circuit breaker is at least partially determinative of the current load at which the circuit breaker will open the electric circuit that it is protecting. A further problem is that many circuit breakers have no manual trip capability such that the circuit breaker can be manually deactivated, for example when it is necessary to shut off a circuit completely for repairs or other maintenance. Additionally, many small circuit breakers, because of the fact that the heater coil is wrapped around the bimetallic strip or, in many cases, the resistance of the bimetallic strip itself may have very low current carrying capabilities and their use is precluded in higher current application situations. Furthermore, the low response speed between an overcurrent pulse and the opening of the circuit with heater/bimetal construction is very slow. It has been found that at least several seconds are required before the circuit is opened and where a human operator may have unintentionally shortcircuited certain equipment, it is desirable to protect him by opening the circuit after only a small amount of current has passed which requires an extremely fast response, on the order of milliseconds. Finally, many circuit breakers in the past have suffered from the failing that if the reset plunger is held in, the circuit breaker is prevented from breaking the circuit and will then result in an overcurrent situation in the component that would otherwise be protected.
It is therefore an object of the present invention to provide a circuit breaker which has self-cleaning and self-aligning contacts.
Another object of the instant invention is a circuit breaker that is compensated for changes in the ambient temperature of the circuit breaker such that the amount of current required to actuate the circuit breaker is not significantly affected.
Still another object of the present invention is to provide a manual trip capability such that the circuit breaker can be manually disengaged.
Another object of this invention is to provide a high shortcircuit capability such that large current loads can be carried by the circuit breaker without effecting its sensitivity to operational control currents.
A still further object of this invention is to provide a circuit breaker with an extremely high response speed to protect against immediate current overloads.
Another object is to provide a circuit breaker which cannot be manually overridden.